42 research outputs found
Waveguide propagation of light in polymer porous films filled with nematic liquid crystals
We theoretically analyze the waveguide regime of light propagation in a
cylindrical pore of a polymer matrix filled with liquid crystals assuming that
the effective radial optical anisotropy is biaxial. From numerical analysis of
the dispersion relations, the waveguide modes are found to be sensitive to the
field-induced changes of the anisotropy. The electro-optic properties of the
polymer porous polyethylene terephthalate (PET) films filled with the nematic
liquid crystal 5CB are studied experimentally and the experimental results are
compared with the results of the theoretical investigation.Comment: 15 pages, 10 figures, revtex4-
Effects of polarization azimuth in dynamics of electrically assisted light-induced gliding of nematic liquid-crystal easy axis
We experimentally study the reorientation dynamics of the nematic liquid
crystal easy axis at photoaligned azo-dye films under the combined action of
in-plane electric field and reorienting UV light linearly polarized at varying
polarization azimuth, . In contrast to the case where the light
polarization vector is parallel to the initial easy axis and , at
, the pronounced purely photoinduced reorientation is observed
outside the interelectrode gaps. In the regions between electrodes with
non-zero electric field, it is found that the dynamics of reorientation slows
down with and the sense of easy axis rotation is independent of the
sign of .Comment: revtex-4.1, 4 pages, 3 figure
Photoinduced reordering in thin azo-dye films and light-induced reorientation dynamics of nematic liquid-crystal easy axis
We theoretically study the kinetics of photoinduced reordering triggered by
linearly polarized (LP) reorienting light in thin azo-dye films that were
initially illuminated with LP ultraviolet (UV) pumping beam. The process of
reordering is treated as a rotational diffusion of molecules in the light
intensity-dependent mean-field potential. The two dimensional diffusion model
which is based on the free energy rotational Fokker-Planck equation and
describes the regime of in-plane reorientation is generalized to analyze the
dynamics of the azo-dye order parameter tensor at varying polarization azimuth
of the reorienting light. It is found that, in the photosteady state, the
intensity of LP reorienting light determines the scalar order parameter (the
largest eigenvalue of the order parameter tensor), whereas the steady state
orientation of the corresponding eigenvector (the in-plane principal axis)
depends solely on the polarization azimuth. We show that, under certain
conditions, reorientation takes place only if the reorienting light intensity
exceeds its critical value. Such threshold behavior is predicted to occur in
the bistability region provided that the initial principal axis lies in the
polarization plane of reorienting light. The model is used to interpret the
experimental data on the light-induced azimuthal gliding of liquid-crystal easy
axis on photoaligned azo-dye substrates.Comment: 27 pages, 11 fugure
Pan-Eurasian Experiment (PEEX): Towards a holistic understanding of the feedbacks and interactions in the land-Atmosphere-ocean-society continuum in the northern Eurasian region
The northern Eurasian regions and Arctic Ocean will very likely undergo substantial changes during the next decades. The Arctic-boreal natural environments play a crucial role in the global climate via albedo change, carbon sources and sinks as well as atmospheric aerosol production from biogenic volatile organic compounds. Furthermore, it is expected that global trade activities, demographic movement, and use of natural resources will be increasing in the Arctic regions. There is a need for a novel research approach, which not only identifies and tackles the relevant multi-disciplinary research questions, but also is able to make a holistic system analysis of the expected feedbacks. In this paper, we introduce the research agenda of the Pan-Eurasian Experiment (PEEX), a multi-scale, multi-disciplinary and international program started in 2012 (https://www.atm.helsinki.fi/peex/). PEEX sets a research approach by which large-scale research topics are investigated from a system perspective and which aims to fill the key gaps in our understanding of the feedbacks and interactions between the land-Atmosphere-Aquatic-society continuum in the northern Eurasian region. We introduce here the state of the art for the key topics in the PEEX research agenda and present the future prospects of the research, which we see relevant in this context